Coal pulverizing apparatus



July 14, 1959 E: c. MILLER 2,894,696 com. PULVERIZING APPARATUS FiledAug. 23, 1957 ll //I 'l/l/ INVENTOR. [mus 6. MILLER United States PatentCOAL PULVERIZKNG APPARATUS Earle C. Miller, Worcester, Mass, assignor toRiley Stoker Corporation, Worcester, Mass, a corporation ofMassachusetts Application August 23, 1957, Serial No. 679,834

6 Claims. (Cl. 241-43) In the pulverizing of coal and other similarfuels for burning in furnaces and the like, it is common practice topass the fuel along with a supply of so-called primary air into thepulverizer for comminution. The primary air supplied has been previouslyraised in temperature by passage through an air heater in heat transferrelationship to the discharge gases from the furnace. At certain times,however, a fuel is encountered which contains a great deal of water. Theonly way that this wet fuel can be properly pulverized is to have thewater removed by evaporation into the primary air. For this purpose itis customary to raise the temperature of the primary gas even higherwhen wet fuel is encountered. Several ways are known by which this maybe accomplished; one of these is the so-called furnace tap; by thisprocess a supply of gas is withdrawn from the furnace and is introducedinto the primary air duct adjacent the pulverizer. The difficultyexperienced with the use of the furnace tap is that it requires a veryfavorable duct arrangement to prevent the accumulation of ash. It alsorequires a high suction within the duct in order to pull the gases outof the furnace. Another way of assuring an addition to the temperatureof the primary air in the event of wet fuel is by the use of a secondaryair heater; the secondary air heater has the disadvantage,

of course, that it involves an added piece of expensive equipment whichin many installations cannot be justified because of the infrequentappearance of wet fuel. These and other difiiculties experienced in thepast with prior art devices have been obviated by the present inventionin a novel manner.

It is, therefore, an outstanding object of the invention to provide apulverizer arrangement in which means is provided for adding to thetemperature of the primary air in the event of wet fuel, which means isinexpensive to manufacture, requires little maintenance, and can bereadily added to existing installations.

It is another object of this invention to provide a pulverizer apparatuswhich may be used satisfactorily with wet fuel even before the boilerhas started up.

A still further object of the present invention is the provision of apulverizer means which will not increase the forced draft or induceddraft fan power and which will not influence the normal heat balance ofthe equipment.

Another object of this invention is the provision of a pulverizerapparatus in which means is provided for increasing the temperature ofthe primary air when wet fuel is encountered, which means does notcreate a hazard or nuisance by introducing ash into the duct system.

It is a still further object of the instant invention to provide meansassociated with a pulverizer for increasing the temperature of theprimary air, which means constitutes a positive source of heatindependent of burner operation and independent of furnace passlocation; by use of this means, the extra heat is instantaneouslyavailable and is not dependent on boiler load, as is the case in afurnace tap .and in a secondary air heater arrangement.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered in the claims appendedhereto.

The character of the invention, however, may be best understood byreference to one of its structural forms, as illustrated in theaccompanying drawing in which:

The single figure is a longitudinal, vertical, sectional View of apulverizer apparatus embodying the principles of the present invention.

Referring to the drawing, which shows the general features of theinvention, the pulverizer arrangement, indicated generally by thereference numeral 10, is shown as consisting of a pulverizer 11, of theball mill type, associated with a crusher-drier 12 of the type shown anddescribed in US. Patent No. 2,647,695. The crusherdrier 12 is of thetype through which fuel and air may be passed and in which revolvinghammers crush the coal and mix it thoroughly with the air forflash-drying of the fuel. The pulverizer 11 is of the ball-tube type,consisting of a generally cylindrical housing 13 mounted on trunnionswhich are revolved by means 'of a motor 14. One end of the mill 11 ismounted in a bearing 15, and is provided with an axial inlet 16. Theother end, through which the mill is driven, is provided with an outlet17. A supply of balls 18 rests in the lower part of the mill and bringsabout the comminution of the fuel. A fuel-feeding device 19 overlies thecrusher-drier and is connected by means of a conduit 21 to a primary airconduit 22, both of which terminate above the crusher-drier 12. Aby-pass 23 extends around the crusher-drier and a pivoted vane 24determines how .much air and fuel will by-pass the crusher-drier. The

outlet of the crusher-drier and the by-pass conduit 23 are joined andconnected by a conduit 25 to the inlet 15 of the mill 11. The outlet 17of the mill is connected by a conduit 26 to an existing fan 27, whoseoutlet is con nected through a valve 28 and through a conduit 29, to thefurnace burners, not shown. A centrifugal separator 31 is located in theconduit 26 between the mill and the fan 27. A mill level control 34 isassociated with the feeder 19 and with the mill 11, and consists of apick-up 35 which extends into the mill and has a dependent portion whichresides near the level of material in the mill. This pick-up issurrounded by a housing 36 which is open to the mill space well abovethe level of material. A source of air under pressure is connectedthrough a valve 37 and an air flow measuring device 38 to a line 39which is connected to the pick-up 35. The line 39 is also connected to amill-level control 41, while a similar line 42 connects the housing 36to the control. A hydraulic linear actuator 43 is mechanically connectedto the control handle 44 of the feeder 19. Hydraulic lines 45 and 46 areconnected to opposite ends of the cylinder 43 and, at their outer ends,to the mill-level control 41.

The duct 22 extends horizontally away from the connection to thecrusher-drier 12 and then vertically for connection to the air heater ofa steam generating unit. In the vertical portion is located a vacuumdamper 47 which is actuated by a crank arm 48 connected to the pistonrod 49 of a hydraulic linear actuator 51. The actuator 51 is connectedby hydraulic lines 52 and 53 to vacuum control 54 which receives itssignal through a line 55 which is connected to a temperature measuringdevice 56 located in the horizontal portion of the duct 22, just aheadof the crusher-drier.

An oil burner 57 of the short-flame type is mounted in the wall of theduct 22 in such a position as to fire along the horizontal portionthereof. An oil control valve 58 is located at the outer end of theburner and is actuated through a linkage 59. The linkage is connected tothe piston rod 61 by a hydraulic linear actuator 62. The linear actuatoris connected by hydraulic lines 63 and 64; to a temperature control 65which receives a signal from a line 66, which signal originates in atemperature measuring device 67 located in the duct 26 between the milland the classifier 31.

A tempering inlet box 68 is located on the vertical portion of the duct22 and is normally covered by a damper 69. The damper is pivoted on theupper part to the box and is actuated by a crank arm 71, Whose other endis connected to a piston rod 61 of the linear actuator 62.

A small blower 72 is connected to the classifier 31 for the operationthereof and a conduit 73 connects the discard portion of the classifierback to the conduit 25 just below the crusher-drier 12, for returningcoarse material from the classifier to the mill.

it is preferable that the burner 57 be of the thermal high-velocity typewhich incorporates a means of vaporizing the oil Within the burner priorto the combustion process; hence, there are no liquid droplets of oil tobe caught and the products of combustion leave the burner as anon-luminous stream of gases with visible length of flame less than atmaximum output. Although the refractory walls of the burner will notexceed 2500 F. in temperature, it is recommended that a heat-resistantsteel duct lining be used in the vicinity of the burner front.

The burner 57 is provided with a blower 74, mounted thereover andconnected through a control damper 75 to the burner. The linkage 59 isconnected to the damper '75 for the actuation thereof by means of an arm76.

The operation of the apparatus will now be readily understood, in viewof the above description. Fuel enters the system through the fuel feeder19, the amount of coal being regulated by the setting of the actuatinghandle 34. The fuel passes down through conduit 21 which it meets theincoming air in the conduit 22. The air in the conduit 22 has passedthrough the air heater of the steam generating unit which the furnaceserves. The fuel and air mix at the end of the conduit 22 and themixture may either pass downwardly through the bypass conduit 23, orthrough the crusher-drier l2, depending on the setting of the damper 24.The fuel-air mixture which passes through the conduit 23 is not treated,but that which passes through the crusher-drier 12 is subjected to aviolent agitation and partial comminution, combined with a dryingeffect. Surface water on the coal is evaporated into the air and thenthe mixture passes through the inlet 25 into the mill 1!. The mill isrotated slowly by means of the motor 14 and the balls 18 are rotatedupwardly until they fall downwardly into the mass of material in thebottom of the mill. By this comminuting action the coal is crushed intoa fine dust which in turn is picked up by the air which flows throughthe upper part of the chamber. This air-coal mixture leaves the millthrough the outlet 17 and passes upwardly into the conduit 26. In theclassifier 31 the coarser particles of fuel are separated out andreturned through the conduit 23 to the entrance of the mill forre-treatment. The air and fine particles pass through the fan 27upwardly through the valve 28 and the conduit 29 to the burners of thefurnace. The amount of mixture of fuel and balls 18 in the bottom of themill 11 is quite important, since too little of the mixture means thatthe capacity of the mill is not being used, and too much of the mixtureclogs the mill and inhibits the production of the proper percentage offine particles. The signal in the conduit 34 which is connected to thehousing 36 represents an air suction pressure inside the mill housing13, well above the level of the fuel and balls in the bottom of themill. The pressure in the conduit 39 is at a high value when the milllevel is high enough to shut off the mouth of the pick-up 35. On theother hand, When the level of material in the mill is well below themouth of the pick-up 35, the pressure in the conduit 39 is quite loW.The differences between the air pressures in the conduits 34 and 39 makethemselves felt in the control 41 which sends the proper signal throughthe hydraulic lines 45 and 46 to the hydraulic linear actuator 43, thusmoving the actuating control handle 44 of the feeder 19 and regulatingthe amount of fuel which is fed into the mill. The air flow measuringdevice 38 permits the operator, by use of valve 37, to regulate the flowof air to an amount for which the control 41 has been calibrated.

it is desirable that the amount of negative pressure in the duct 22 becarefully regulated so that the amount of air being introduced and thetemperature of the incoming air is at an optimum value. For thispurpose, the control 5- 3- receives a temperature signal from thetemperature measuring device 56 and transmits a signal through thehydraulic lines 52 and 53 to the linear actuator 51. This in turn actsthrough the piston rod 49 and the crank arm 48 to set the damper 47 at adesired value. It is desirable when the fuel is very wet, to supplementthe heat avialable in the incoming primary air by means of burner 57. Itis well known that warmer air is capable of absorbing more water thancolder air; furthermore, a ball mill tends to clog considerably whenthere is too much surface moisture in the coal. Therefore, when thetemperature measuring device 67 in the duct 28 which measures thetemperature of the output air of the mill indicates that the temperatureis low, it sends a signal to that effect through the line 66 to thecontrol 65. It is a fact that the output air temperature will be lowerwhen the water in the coal is higher because of the absorption of heatby the water in evaporating. A low temperature, therefore, in duct 26indicates that the fuel entering the mill is wet and it would bedesirable to use a higher temperature primary air in the duct 22. Thesignal to that effect is transmitted by the control 65 through thehydraulic lines 63 and 64 to the linear actuator 62. The hydraulicpressure is such that the piston rod 61 will be drawn downwardly. Thisacts through the linkage 59 to increase the amount of oil flowingthrough the valve 58 to the burner 57 and, at the same time, adjusts thedamper 75 by means of the arm 76 so that a greater amount of air flowsinto the burner; the burner heat is thus increased. At the same time,the damper 69 is closed so that there will be very little tempering airentering the system. This brings about an increase in the temperature ofthe primary air passing into the mill. A rise in temperature of theproper amounts in the conduit 26 will make itself known to thetemperature measuring device 67 and eventually will cause the piston rod61 ot rise, shutting off air and oil passage to the burner S9 andcutting down its firing rate and, at the same time, opening the damper69 to admit small amounts of tempering air into the duct.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come within the scope claimed.

The invention having been thus described, what is claimed as new, anddesired to secure by Letters Patent, is:

l. A coal pulverizing apparatus, comprising a comminuting mill, a coalfeeder, an air duct, a crusher-drier, the feeder and the duct beingconnected to mix the air and coal, the crusher-drier connecting thefeeder and duct to the mill for drying the coal, a by-pass conduit alsojoining the duct and feeder to the mill, means for causing the coal-airmixture to pass either through the crusherdrier or through the by-passconduit, a burner mounted to fire directly into the duct, a temperingdamper in the said duct, and means controlled by the temperature of thecoalair mixture leaving the mill to regulate the rate of firing of theburner and the amount of tempering air admitted by the tempering damper.

2. A coal pulverizing apparatus, comprising a comminuting mill, a coalfeeder, an air duct, a crusher-drier, the feeder and the duct beingconnected to mix the air and coal, the crusher-drier connecting thefeeder and duct to the mill for drying the coal, a by-pass conduit alsojoining the duct and feeder to the mill, means for causing the coal-airmixture to pass either through the crusher-drier or through the by-passconduit, a burner mounted to fire directly into the duct, a temperingdamper in the said duct, an indicating device located in the outlet ofthe mill for measuring the temperature of the coalair mixture leavingthe mill, a controller to which the device is connected, an actuatorconnected to the controller and acting to regulate the rate of firing ofthe burner and the amount of tempering air admitted by the temperingdamper.

3. A coal pulverizing apparatus, comprising a comminuting mill, a coalfeeder, a level control including a measuring device located in the milland connected to the feeder to maintain the feeding rate at such a valueas to maintain the level of coal in the mill at a preselected Value, anair duct, a crusher-drier connecting the feeder and duct to the mill fordrying the coal, a by-pass conduit also joining the duct and feeder tothe mill, means for causing the coal-air mixture to pass either throughthe crusherdrier or through the by-pass conduit, a burner mounted tofire directly into the duct, a tempering damper in the said duct, andmeans controlled by the temperature of the coal-air mixture leaving themill to regulate the rate of firing of the burner and the amount oftempering air admitted by the tempering damper.

4. A coal pulverizing apparatus, comprising a comminuting mill, a coalfeeder, an air duct, :1 crusher-drier, the feeder and the duct beingconnected to mix the air and coal, the crusher-drier connecting thefeeder and duct to the mill for drying the coal, a by-pass conduit alsojoining the duct and feeder to the mill, means for causing the coal-airmixture to pass either through the crusher-drier or through the by-passconduit, a burner mounted to first directly into the duct, a temperingdamper in the said duct, a vacuum damper in the air duct ahead of theburner, a temperature-measuring apparatus located in the duct at aposition following the burner, a controller connected to thetemperature-measuring apparatus and to the vacuum damper to regulate thetemperature of the air, and means controlled by the temperature of thecoal-air mixture leaving the mill to regulate the rate of firing of theburner and the amount of tempering air admitted by the tempering damper.

5. A coal pulverizing apparatus, comprising a comminuting mill, a coalfeeder, a level control including a measuring device located in the milland connected to the feeder to maintain the feeding rate at such a valueas to maintain the level of coal in the mill at a preselected value, anair duct, a crusher-drier, the feeder and the duct being connected tomix the coal and air, the crusher-drier connecting the feeder and theduct to the mill for drying the coal, a by-pass conduit also joining theduct and feeder to the mill, means for causing the coal-air mixture topass either through the crusher-drier or through the by-pass conduit, aburner mounted to fire directly into 'the duct, a tempering damper inthe said duct, a vacuum damper in the air duct ahead of the burner, atemperature-measuring apparatus located in the duct at a positionfollowing the burner, a controller connected to thetemperature-measuring apparatus and to the vacuum damper to regulate thetemperature of the air, and indicating device located in the outlet ofthe mill for measuring the temperature of the coal-air mixture leavingthe mill, a controller to which the device is connected, an actuatorconnected to the controller and acting to regulate the rate of firing ofthe burner and the amount of tempering air admitted by the temperingdamper.

6. A coal pulverizing apparatus, comprising a comminuting mill, a coalfeeder, an air duct, a crusher-drier, the feeder and the duct beingconnected to mix the air and coal, the crusher-drier connecting thefeeder and duct to the mill for drying the coal, a by-pass conduit alsojoining the duct and feeder to the mill, means for causing the coalairmixture to pass either through the crusher-drier or through the by-passconduit, a burner mounted to fire directly into the duct, a valvecontrolling the amount of fuel admitted to the burner, a temperingdamper in the said duct, an indicating device located in the outlet ofthe mill for measuring the temperature of the coal-air mixture leavingthe mill, a controller to which the device is connected, an actuatorconnected to the controller on the one hand and to the valve and thetempering damper on the other hand to regulate the rate of firing of theburner and the amount of tempering air admitted by the tempering damper.

References Cited in the file of this patent UNITED STATES PATENTS2,716,002 Craig Aug. 23, 1955

